1. Technical Field
The present invention relates to a vehicle occupant protection apparatus and, in particular, to an initiator for an inflator for an air bag or other inflatable occupant protection device.
2. Description of the Prior Art
European Patent Application EP 0 903 487 A2 describes an integrated pulsed propulsion system for a microsatellite and, in particular, a micro thruster for a microsatellite. The microthruster is formed with a chamber closed by a diaphragm, which acts as a blow-out disk. A fluid, such as an inert gas, is disposed within the chamber. Heating of the gas causes the gas pressure to increase until the diaphragm ruptures, which, in turn, causes the gas to flow out of the chamber. The flowing gas acts as a propellant, and provides a small unit of force. The microthruster is adapted to be formed by known batch processing methods with 104 to 106 microthrusters per wafer. The unit of force can be scaled by varying the number of microthrusters used for an application, the geometry of the chamber, and the type of fluid used within the chamber.
The microthruster described in EP 0 903 487 A2 is described elsewhere in the literature as consisting of a 3-layer sandwich. The top layer contains an array of thin diaphragms (0.5 micron thick silicon nitride, 190 or 290 or 390 microns square). The middle layer contains an array of through-holes (Schott FOTURAN(copyright) photosensitive glass, 1.5 mm thick, 300, 500, or 700 micron diameter holes), which are loaded with propellant. The bottom layer contains a matching array of polysilicon micro-resistors. The bottom two layers are bonded together, propellant is added to the middle layer, and then the top layer is bonded to complete the assembly. With different sizes of plenum holes, diaphragms, and resistors, many different configurations can be assembled.
This type of microthruster is one type of device known in the art as a xe2x80x9cmicroelectromechanical system devicexe2x80x9d, or xe2x80x9cMEMS devicexe2x80x9d. This type of device is known for use in a variety of applications. For example, U.S. Pat. No. 5,880,921 discloses a monolithically integrated switched capacitor bank using MEMS technology.
The present invention is an initiator for actuating an inflation fluid source for an inflatable vehicle occupant protection device. The initiator comprises a plurality of electrically energizable microelectromechanical system (MEMS) devices.
In one embodiment, the MEMS devices are associated in a one to one relationship with chambers containing ignitable material. Each one of the MEMS devices, when energized, generates combustion products, including heat, for igniting the associated ignitable material. At least one terminal pin is electrically connected with the plurality of MEMS devices for receiving an electric signal for energizing at least one of the MEMS devices.
In another embodiment, the inflation fluid source comprises a solid body of ignitable material in a housing for, when ignited, generating inflation fluid for inflating the protection device. The MEMS devices are at spaced locations adjacent the body of ignitable material and, when energized, fracture the body ignitable material at the spaced locations.
In another embodiment, the MEMS devices are supported at predetermined locations adjacent a burst disk and are selectively energizable to make an opening of a selected configuration in the burst disk.
In another embodiment, the inflation fluid source is located in a chamber. An actuation module in the chamber includes a plurality of individually energizable microelectromechanical system (MEMS) devices. The actuation module also includes a receiver for receiving a control signal from outside the chamber for energizing at least one of the MEMS devices to actuate the inflation fluid source. The inflator is free of wires extending into the chamber.
In another embodiment, the initiator comprises a first plurality of MEMS devices for opening a burst disk and a second plurality of MEMS devices for igniting an ignitable material.